Usually appears for me when I restart the application. Dodgy fix from simhq forums (
here) by Bokononist:
Yea Frey, it is a weird one. I've had this one a few times, especially the servers not appearing at all.
The work around is this.
1. Click on server, set up your machine as a server with all the default options. Start the server.
2. Once its started stop it as quickly as possible to stop the mass unwashed trying to log on to your machine.
3. Click client and log on to the server of your choice.
Don't know why this works, but I have ATAG_Bliss to thank for this one, glad to pass it on. If this works for you post back and let me know.
Cheers,
Boko